KX3 Heatsink discussion

[Jan-10]

I'm puzzled by the comment posted yesterday:  by Jim W7JR

""I've been doing a lot of FT-8 using my KX3 and my KXPA100 at 20 watts,
and have noticed that the KX3 is heating up quite a bit and is almost
hot to the touch""

Why should the KX3 be heating up, when the AMP is running only 20W ?
Is the KX3 "drive" not backed-down at this level ?? HELP

Cheers, Jan K1ND

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[Jim Brown-10]

A well designed output stage SHOULD be hot to the touch. The temperature
component of protection in Elecraft output stages seems to kick in when
the internal temperature approaches 70 deg C.  You can see this, for
example, by watching temperature in the KPA500 and listening to fan
speed. The function of the heat sink is to act as a conductor between
the semiconductor junctions and the surrounding environment, and
increased mass acts as a sort of buffer.

73, Jim K9YC

On 8/5/2017 2:53 PM, Jan wrote:
> ""I've been doing a lot of FT-8 using my KX3 and my KXPA100 at 20 watts,
> and have noticed that the KX3 is heating up quite a bit and is almost
> hot to the touch""
>
> Why should the KX3 be heating up, when the AMP is running only 20W ?
> Is the KX3 "drive" not backed-down at this level ?? HELP


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[wayne burdick]

The KX3 and KX2 max heat sink temperature is 63 C. At that point power is automatically dropped to 5 W. If it reaches the max temp again, transmit is exited.

Wayne
N6KR

> On Aug 6, 2017, at 10:27 AM, Jim Brown <[hidden email]> wrote:
>
> A well designed output stage SHOULD be hot to the touch. The temperature component of protection in Elecraft output stages seems to kick in when the internal temperature approaches 70 deg C.  You can see this, for example, by watching temperature in the KPA500 and listening to fan speed. The function of the heat sink is to act as a conductor between the semiconductor junctions and the surrounding environment, and increased mass acts as a sort of buffer.
>
> 73, Jim K9YC
>
> On 8/5/2017 2:53 PM, Jan wrote:
>> ""I've been doing a lot of FT-8 using my KX3 and my KXPA100 at 20 watts,
>> and have noticed that the KX3 is heating up quite a bit and is almost
>> hot to the touch""
>>
>> Why should the KX3 be heating up, when the AMP is running only 20W ?
>> Is the KX3 "drive" not backed-down at this level ?? HELP
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
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[wayne burdick]

Actually, that’s 63 C at the PA device location on the PC board. The outside surface of the heat sink itself is quite a bit lower in temperature.

Wayne
N6KR

> On Aug 6, 2017, at 11:39 AM, Wayne Burdick <[hidden email]> wrote:
>
> The KX3 and KX2 max heat sink temperature is 63 C. At that point power is automatically dropped to 5 W. If it reaches the max temp again, transmit is exited.
>
> Wayne
> N6KR
>
>
>
>> On Aug 6, 2017, at 10:27 AM, Jim Brown <[hidden email]> wrote:
>>
>> A well designed output stage SHOULD be hot to the touch. The temperature component of protection in Elecraft output stages seems to kick in when the internal temperature approaches 70 deg C.  You can see this, for example, by watching temperature in the KPA500 and listening to fan speed. The function of the heat sink is to act as a conductor between the semiconductor junctions and the surrounding environment, and increased mass acts as a sort of buffer.
>>
>> 73, Jim K9YC
>>
>> On 8/5/2017 2:53 PM, Jan wrote:
>>> ""I've been doing a lot of FT-8 using my KX3 and my KXPA100 at 20 watts,
>>> and have noticed that the KX3 is heating up quite a bit and is almost
>>> hot to the touch""
>>>
>>> Why should the KX3 be heating up, when the AMP is running only 20W ?
>>> Is the KX3 "drive" not backed-down at this level ?? HELP
>>
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email]
>

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